Light Timing Study

Study Summary

Chronic circadian misalignment and sleep restriction peak during late adolescence, and are associated with morning daytime sleepiness, poor academic performance, conduct problems, depressed mood, suicidal ideation, substance use, insulin resistance, and obesity. Bright light exposure from light boxes can shift rhythms earlier (phase advance) to facilitate earlier sleep onset and reduce morning circadian misalignment and the associated risks. To phase advance circadian rhythms, the investigators' PRCs showed that the ideal time to begin light exposure was slightly before wake-up time and light should be avoided around bedtime because this is when light produces maximum phase delay shifts. An unexpected finding from these results, however, was a second advancing region in the afternoon (\~6 to 9 h after habitual wake-up time) suggesting that afternoon light may have more circadian phase advancing ability than traditionally thought. The overall goal of this mechanistic study is to follow-up on the unexpected PRC findings and test whether individually-timed afternoon light alone and in combination with morning bright light can shift circadian rhythms earlier in older adolescents. Four groups will be compared in a randomized parallel group design: afternoon bright light, morning bright light, morning + afternoon bright light, and a dim room light control. Adolescents will complete a 2-week protocol. After a baseline week with a stable sleep schedule, adolescents will live in the laboratory for 7 days. Sleep/dark and the time of bright light exposure will gradually shift earlier. Bright light (\~5000 lux) will be timed individually based on his/her stable baseline sleep schedule. The first 3-h morning bright light exposure will begin 1 h before wake on the first morning. The first 3-h afternoon bright light exposure will begin 5 h after wake. The morning + afternoon exposures will begin at the same times, but each exposure will be 1.5 h so that a total of 3 h of bright li

Primary Outcome

Saliva sampling for the baseline DLMO will begin 6 hours before baseline bedtime and end 2 hours after baseline bedtime to capture the rise of endogenous melatonin. Sampling for the final DLMO will begin 7 hours before baseline bedtime and end 2 hours after baseline bedtime. Participants remain awake and seated in comfortable recliners in dim light (\< 5 lux), except when they need to use the adjoining restroom (also \< 5 lux). Saliva samples are collected every 30 minutes using Salivettes, The

Conditions Studied

Interventions

• BEHAVIORAL Baseline Sleep Satiation and Phase Stabilization
• BEHAVIORAL Gradually Shifted Sleep

Study Locations (1)